BOSTON If driving between Boston and Cambridge these days seems more difficult than ever before, you’re not imagining things. On a simple 15-minute commute along Memorial Drive, you’ll likely run into multiple detours: the Anderson Bridge, Western Avenue, the Reid Overpass by the BU Bridge.

Reid Overpass

During the morning rush, traffic is backed up by the BU Bridge because of the closed Reid Overpass. (Asma Khalid/WBUR)

The roundabout by the BU Bridge is a test of patience for drivers. Road crews began construction on the Memorial Drive overpass unexpectedly this past Sunday.

During a routine bridge inspection, engineers discovered the bridge was “structurally deficient.” It had holes, gaping holes, the kind in which you can see daylight poking through if you stand under it.

“There was enough missing material,” DePaola added. “The concern was if there was ever essentially a backup, a nose-to-tail backup across the bridge, sections might collapse.”

So the overpass was shut down. Now, all the through traffic on Memorial Drive needs to reroute and join the local traffic in the roundabout. Construction could take up to six months, but road crews are working double shifts to complete the project as soon as possible.

Charles River Bridges

Back in 2007 an eight-lane bridge in Minnesota collapsed, killing 13 people and injuring 145 others. Because of that tragedy, lawmakers here in Massachusetts agreed they needed to fix the state’s own aging infrastructure, DePaola says.

“[Lawmakers] charged us with reducing the number of structurally deficient bridges in the state,” he said. “What they did is they said, ‘Here’s $3 billion. And you have to do it in eight years, by 2016.’ ”

That funding timeline is why so many bridges are under construction almost simultaneously. Within six years, six bridges connecting Boston to Cambridge will be fixed.

The funny thing about these two cities is that they need the Charles River bridges to survive economically. Every afternoon during rush hour more than 23,000 cars cross the bridges in just one hour. That heavy traffic is why almost all of the bridges need fixing.

First, it was the Craigie and BU bridges in 2010. Now, it’s the Anderson Bridge, opposite Harvard’s Kennedy School of Government.

Traffic Woes

Western Avenue construction (Asma Khalid/WBUR)

Lauren Dahlin drives from Cambridge to Boston College every morning. As she passed Western Avenue, she points out the roadwork.

“It just seems like really poor planning that they would, you know, choose to do construction on both places that could possibly lead you out of Cambridge, or at least this part of Cambridge,” she said.

So, I ask the city of Cambridge: Why repair Western Avenue when the Charles River bridges are already under construction?

“We have water mains and sewer and drain lines that were really constructed in the 1870s, and so they’re in significant need of upgrading and reconstruction,” said Kathy Watkins, supervising engineer with the city’s Department of Public Works. “So it’s not one we felt like we could sort of put off for, you know, five, six, seven years while these other projects continued.”

Dahlin says the traffic makes her so frustrated, she’s considered moving out of Cambridge.

“There is a sign that says ‘Expect delays: two years.’ What does that even mean?” she lamented. “When did the two years start? When does two years end? And, it’s extremely demoralizing every time you go by it because you’re stuck in traffic and then it says, ‘Expect delays: two years.’ ”